1. Field of the Invention
The present invention relates to a control apparatus and a control method for an internal-combustion engine, and more particularly, to an apparatus and a method for determining whether a crankshaft is rotating in a forward direction or a reverse direction and detecting a crank angle based on the determined crankshaft rotating direction.
2. Description of Related Art
Hitherto, there has been known a control apparatus for an internal-combustion engine adapted to detect a reverse rotation of an internal-combustion engine before the stopping of the engine and then detect a crank angle at the time of stopping the engine. Fuel injection and ignition are started at an early stage after the starting of engine and, in order to improve the starting performance of the internal-combustion engine, the crank angle at the time of stopping the engine is stored, and at the time of restarting the engine, the crank angle is estimated by using the stored crank angle at the time of stopping the engine as an initial value. Based on the estimated crank angle, the fuel injection and the ignition are started. At the time of stopping the engine, the internal-combustion engine rotates in a reverse direction once before the stopping of the engine due to the pressure in a combustion chamber (refer to, for example, Japanese Laid-Open Patent Publication No. 2006-233914).
Meanwhile, as a method for determining whether an internal-combustion engine is rotated in the forward or the reverse direction, there is a method in which a rotation sensor (crank angle sensor), which outputs a pulse signal synchronized with the rotation of a crankshaft, is provided, and the pulse width and amplitude of the pulse signal are adapted to change according to whether a rotating direction of the engine is in the forward direction or the reverse direction. The measured values of the pulse width and amplitude are compared with threshold values thereof, so that whether the engine is rotated in the forward direction or the reverse direction is determined.
However, variations, deterioration or the like of the rotation sensor or circuits that process rotation signals leads to variations in the pulse width and amplitude at the time of a forward rotation or a reverse rotation, resulting in deteriorated accuracy of determining a rotating direction of the engine. Hence, there is a possibility of incorrectly determining whether the internal-combustion engine (crankshaft) is rotated in the forward direction or the reverse direction.
Furthermore, the incorrect determination of a rotating direction of the engine immediately before the stopping of the engine causes incorrect detection of a crank angle at the time of the stopping of the engine, and the crank angle immediately after the starting of the engine is estimated on the basis of the information on the incorrect stop position. Controlling the fuel injection and ignition based on the estimation result raises a problem in that fuel injection or ignition is set on a wrong cylinder, causing the occurrence of abnormal combustion, such as afterburning or backfire, or deteriorated exhaust property or starting performance.